The AM2 model proposed by Bernad et al. [O. Bernad, Z. Hadj-Sadok, D. Dochain, A. Genovesi, J.P. Steyer, Dynamical model development and parameter identification for an anaerobic wastewater treatment process, Biotechnol. Bioeng. 75 (4) (2001) 424-438] was developed as a simple model to simulate wastewater anaerobic digestion. In order to apply this model to a full scale UASB reactor, global COD balance was done. This allows us to determine the stoichiometric coefficients. Using an asymptotic observer biomass content estimation was done without knowledge about the reaction kinetics. Then, a decoupled parameter estimation procedure was followed to determine the evolution of specific growth coefficients. The model and parameters validation was done using experimental data of methane production. (c) 2008 Elsevier B.V. All rights reserved.